Power system having efficiency-based speed control

ABSTRACT

A power system is disclosed as having a power source, a transmission configured to receive a torque output from the power source and to drive a traction device, and an operator input device. The power system may also have a controller configured to reference a signal from the operator input device with a map stored in memory to determine a corresponding speed of the power source, and to determine a margin between an actual and a maximum available torque output of the power source at a current speed. The controller may also be configured to selectively adjust a speed of the power source mapped to the maximum displaced position of the operator input device based on the margin, and to selectively adjust fueling of the power source at a current displacement position of the operator input device and operation of the transmission based on the signal and map.

TECHNICAL FIELD

The present disclosure is directed to a power system and, moreparticularly, to a power system having efficiency-based engine speedcontrol.

BACKGROUND

Machines, such as wheel loaders, dozers, and other heavy equipment, areused to perform many tasks. To effectively perform these tasks, themachines require an engine that provides significant torque through atransmission to one or more tires. In order to control the speed and/ortorque of the tires, the operator of these machines is typicallyprovided with one or more different foot pedals. For example, a rightfoot pedal can be used to affect engine fueling, while a left foot pedalcan be used to affect machine braking. Additional foot pedals may beavailable in some applications to control connection of the engine tothe transmission.

Although the typical foot pedal configuration may be suitable when amechanical step-change transmission is utilized to transmit power fromthe engine to the tires, it may be insufficient when a continuouslyvariable transmission (CVT) is utilized. A CVT is an automatic type oftransmission that provides an infinite number of output ratios withinits operating range. A hydraulic CVT includes a pump and a fluid motorthat receives pressurized fluid from the pump. Depending on a dischargeflow rate and pressure of the pump and a displacement of the motor, themotor speed and output torque at the tires may be varied. An electricCVT includes a generator and an electric motor that receives currentfrom the generator. Depending on the current supplied to the motor, themotor speed and output torque may be varied. When using a CVT, the goalis to keep the engine at the most efficient speed while still providingthe necessary power to meet the operator's commands. In this situation,the strategy described above of changing only engine fueling in directresponse to operator input may work against the efficiency goal.Therefore, an alternative strategy is required to efficiently controloperation of a machine utilizing a CVT.

An alternative method of machine control is described in U.S. PatentPublication No. 2008/0103019 of Cronin et al. that published on May 1,2008 (the '019 publication). Specifically, the '019 publicationdescribes a continuously variable transmission for a machine. Thecontinuously variable transmission includes a driven element, a firstoperator interface device, a second operator interface device, and acontroller. The controller is configured to receive a first displacementsignal associated with the first operator interface device, and a seconddisplacement signal associated with the second operator interfacedevice. The controller is further configured to determine a net operatorinput value as a function of the first and second displacement signals,and to regulate a torque of the driven element in response to thedetermined net operator input value.

Although the system of the '019 publication may provide efficientregulation of a speed-controlled CVT by separating engine speed fromtransmission torque control, it may still be less than optimal. Inparticular, there may be times when engine speed control, in combinationwith transmission torque control, can further improve machineefficiencies. And the system of the '019 publication may not capturethese efficiencies.

The power system of the present disclosure solves one or more of theproblems set forth above.

SUMMARY

One aspect of the present disclosure is directed to a power system foruse with a mobile machine having a traction device. The power system mayinclude a power source configured to generate a torque output, atransmission configured to receive at least a portion of the torqueoutput and to drive the traction device, and an operator input devicemovable through a range from a neutral position to a maximum displacedposition to generate a signal indicative of a desired torque of thetraction device and a desired speed of the power source. The powersystem may also include a controller in communication with the powersource, the transmission, and the operator input device. The controllermay be configured to reference the signal from the operator input devicewith a map stored in memory to determine a corresponding speed of thepower source, and to determine a margin between an actual and a maximumavailable torque output of the power source at a current power sourcespeed. The controller may also be configured to selectively adjust aspeed of the power source mapped to the maximum displaced position ofthe operator input device based on the margin, and to selectively adjustfueling of the power source at a current displacement position of theoperator input device and operation of the transmission based on thesignal and on the map.

Another aspect of the present disclosure is directed to another powersystem power system for a mobile machine having a traction device. Thispower system may include a power source configured to generate a torqueoutput, a continuously variable transmission configured to receive atleast a portion of the torque output and to drive the traction device,and an operator input device movable through a range from a neutralposition to a maximum displaced position to generate a signal indicativeof a desired torque of the traction device and a desired speed of thepower source. The power system may also include a controller incommunication with the power source, the continuously variabletransmission, and the operator input device. The controller may beconfigured to reference the signal from the operator input device with amap stored in memory to determine a corresponding speed of the powersource, and to determine a margin between an actual and a maximumavailable torque output of the power source at a current power sourcespeed. The controller may also be configured to selectively adjust aspeed of the power source mapped to the maximum displaced position ofthe operator input device based on the margin, and to selectively adjustfueling of the power source at a current displacement position of theoperator input device and operation of the continuously variabletransmission based on the signal and on the map. The controller may befurther configured to receive a selection from an operator of the mobilemachine indicative of desired operation in a performance mode or aneconomy mode, and to selectively lower the speed of the power sourcemapped to the maximum displaced position and a speed of the power sourcemapped to the neutral position when the selection is the economy mode.

In yet another aspect, the present disclosure is directed to a method ofoperating a machine having a traction device driven by a power sourcevia a transmission. The method may include determining a displacementposition of an operator input device that is indicative of a desiredtorque of the traction device and a desired speed of the power source,and referencing the displacement position with a map to determine acorresponding speed of the power source. The method may also includedetermining a margin between an actual and a maximum available torqueoutput of the power source at a current speed, and selectively adjustinga speed of the power source mapped to the maximum displaced position ofthe operator input device based on the margin. The method may furtherinclude selectively adjusting fueling of the power source at a currentdisplacement position of the operator input device and operation of thetransmission based on the signal and on the map, and receiving aselection from an operator of the mobile machine indicative of desiredoperation in a performance mode or an economy mode. The method mayadditionally include selectively lowering the speed of the power sourcemapped to the maximum displaced position of the operator input deviceand a speed of the power source mapped to a neutral position of theoperator input device when the selection is the economy mode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic illustration of an exemplary disclosed machine;

FIG. 2 is a pictorial illustration of an exemplary disclosed operatorstation for use with the machine of FIG. 1;

FIG. 3 is a diagrammatic illustration of an exemplary disclosedtransmission system for use with the machine of FIG. 1;

FIG. 4 is an exemplary control map that may be used to control thetransmission system of FIG. 3; and

FIG. 5 is a flowchart depicting an exemplary method of operating thetransmission system of FIG. 3.

DETAILED DESCRIPTION

FIG. 1 illustrates an exemplary machine 10 having multiple systems andcomponents that cooperate to accomplish a task. The tasks performed bymachine 10 may be associated with a particular industry such as mining,construction, farming, transportation, power generation, or any otherindustry known in the art. For example, machine 10 may embody a mobilemachine such as the wheel loader depicted in FIG. 1, a bus, an on- oroff-highway haul truck, or any other type of mobile machine known in theart. Machine 10 may include an operator station 12, one or more tractiondevices 14, and a powertrain 16 operatively connected to drive at leastone of traction devices 14 in response to signals generated withinoperator station 12.

As illustrated in FIG. 2, operator station 12 may include devices thatreceive input from a machine operator indicative of a desired machineoperation. Specifically, operator station 12 may include one or moreoperator interface devices 18 located proximate an operator seat 20.Operator interface devices 18 may initiate movement of machine 10 byproducing displacement signals that are indicative of a desired machinemaneuver and/or mode of operation. In one embodiment, operator interfacedevices 18 include a right foot pedal 18 a and a mode switch 18 b. As anoperator manipulates right foot pedal 18 a, the operator may expect andaffect a corresponding change in machine travel speed and/or rimpulltorque. As the operator pushes or otherwise activates mode switch 18 b,a standard mode or any number of economy modes of operation may beinitiated. It is contemplated that operator interface devices other thana foot pedal and a switches such as, for example, joysticks, levers,wheels, knobs, dials, and other devices known in the art, mayadditionally or alternatively be provided within operator station 12 forcontrol of machine 10, if desired. For example, a dial could be used inaddition to or instead of right foot pedal 18 a to set a desired speed.

As illustrated in FIG. 3, powertrain 16 may be an integral packageconfigured to generate and transmit power to traction devices 14. Inparticular, powertrain 16 may include a power source 22 operable togenerate a power output, a transmission 24 connected to receive thepower output and transmit the power output in a useful manner totraction devices 14, and a control module 27 configured to regulate theoperation of power source 22 and transmission 24 in response to one ormore input (e.g., in response to operator input received via interfacedevices 18).

Power source 22 may include an internal combustion engine havingmultiple subsystems that cooperate to produce mechanical and/orelectrical power output. For the purposes of this disclosure, powersource 22 is depicted and described as a four-stroke diesel engine. Oneskilled in the art will recognize, however, that power source 22 may beany other type of internal combustion engine such as, for example, agasoline or a gaseous fuel-powered engine. The subsystems of powersource 22 may include, for example, a fuel system, an air inductionsystem, an exhaust system, a lubrication system, a cooling system, orany other appropriate system.

Power source 22 may be configured to produce a torque output directed totransmission 24 and to other parasitic loads (e.g., to hydraulicsystems, electrical systems, cooling systems, etc.) through a range ofspeeds. For the purposes of this disclosure, the term Actual EngineTorque may refer to an amount of torque currently being generated bypower source 22 at a given speed. In the disclosed embodiment, ActualEngine Torque corresponds directly with an amount of fuel currentlybeing consumed by power source 22 at the given speed. In other words, ameasurement of the current fueling rate of power source 22 at the givenspeed may be used to determine the Actual Engine Torque. The termAvailable Engine Torque may refer to a maximum amount of torque thatcould be produced at the given speed when right foot pedal 18 a is in afully displaced position. In the disclosed embodiment, Available EngineTorque corresponds directly with a maximum amount of fuel that could bedirected into power source 22. In some embodiments, this maximum amountof fuel may be limited by a maximum torque limit of the engine, a smokelimit of the engine, or another limit known in the art.

One or more sensors 34 may be associated with power source 22 to sensethe speed thereof. In one example, sensor 34 may embody a magneticpickup type of sensor associated with a magnet embedded within arotational component of power source 22 such as a crankshaft orflywheel. During operation of power source 22, sensor 34 may sense arotating field produced by the magnet and generate a signalcorresponding to the rotational speed of power source 22. These signalsmay be directed to control module 27 for further processing.

Transmission 24 may embody, for example, a continuously variabletransmission (CVT). Transmission 24 may be any type of continuouslyvariable transmission, such as a hydraulic CVT, a hydro-mechanical CVT,an electric CVT, or another CVT configuration as would be apparent toone skilled in the art.

A continuously variable transmission generally consists of a drivingelement 26, and a driven element 28 that is powered by driving element26. In the exemplary hydraulic CVT of FIG. 3, driving element 26 is apump, such as a variable displacement hydraulic pump, and driven element28 is a motor, such as a variable displacement hydraulic motorconfigured to receive pressurized fluid from driving element 26. Drivingelement 26 may be connected to drive driven element 28 with pressurizedfluid via one or more different conduits in response to a torque commanddirected to driving and/or driven elements 26, 28 by control module 27.In some situations, driven element 28 may alternatively drive drivingelement 26 in reverse direction, for example during a braking event.

Although described as a hydraulic CVT, transmission 24 couldalternatively embody an electric CVT. In this configuration, drivingelement 26 would embody a generator driven by power source 22, anddriven element 28 would embody a motor mechanically connected totraction device 14 and configured to receive electricity produced by thegenerator. Similar to the hydraulic configuration of transmission 24,the motor of the electric configuration may be powered by the generatorin response to a torque command from control module 27.

Transmission 24 may be at least partially controlled based on input fromright foot pedal 18 a. That is, right foot pedal 18 a is manipulated byan operator, the foot pedal may provide signals signifying a desiredmachine travel speed, and output torque, and/or a desired engine speed.For example, right foot pedal 18 a may have a minimum displaced position(a.k.a., a neutral position) and be movable through a range of positionsto a maximum or fully displaced position. A sensor 32, such as a switchor potentiometer, may be provided in association with right foot pedal18 a to sense the displacement position thereof and producecorresponding signals responsive to the displaced position. Thedisplacement signals from sensor 32 may be directed through controlmodule 27 to transmission 24 to control the torque output of drivenelement 28 and also to power source 22 to control fueling thereof.

For example, as right foot pedal 18 a is displaced to a position furthertoward the fully displaced position, a signal indicative of a desiredincrease in travel speed and/or rimpull torque may be created. Controlmodule 27 may then use this signal, alone or in combination with othersignals (e.g., signals from sensor 34) to determine the torque commandsent to transmission 24 that produces the desired increase in travelspeed. Similarly, as right foot pedal 18 a is displaced toward theneutral position, a signal indicative of a desired decrease in travelspeed and/or rimpull torque may be created and control module 27 may usethis signal to determine a corresponding torque command sent totransmission 24.

In some instances, the torque command directed to transmission 24 maychange without a corresponding change in the displacement position ofright foot pedal 18 a. For example, when traveling at steady state,machine 10 could encounter a hill and begin to speed up or slow down dueto the effects of gravity. In either of these situations, control module27 may sense the undesired change in speed (undesired as nocorresponding change in pedal displacement position would have beensensed) and responsively adjust the torque command directed totransmission 24 in order to maintain the desired speed.

As the ratio of transmission 24 is adjusted based on the torque commandfrom control module 27, transmission 24 may draw varying amounts oftorque from power source 22. In order to ensure that an adequate supplyof power is always available to transmission 24 for unanticipatedtransient conditions, power source 22 may be capable of generating moretorque at a given speed than what is immediately required bytransmission 24. And power source 22 may normally be allowed, withinlimits that will be described in more detail below, to produce about 10%more torque than what is directed to transmission 24 (and to the otherloads of machine 10). That is, the Available Engine Torque may bemaintained at about 10% more than the Actual Engine Torque, withinparticular limits. It should be noted that a different torque margin mayalternatively be utilized, if desired. Control module 27 may beconfigured to regulate the fueling of power source 22, so as to maintainthe desired margin between Available Engine Torque and Actual EngineTorque.

Control module 27 may embody a single microprocessor or multiplemicroprocessors that include a means for controlling the operation ofpowertrain 16 in response to the received signals. Numerous commerciallyavailable microprocessors can be configured to perform the functions ofcontrol module 27. It should be appreciated that control module 27 couldreadily embody a general machine microprocessor capable of controllingnumerous machine functions. Control module 27 may include a memory, asecondary storage device, a processor, and any other components forrunning an application. Various other circuits may be associated withcontrol module 27 such as power supply circuitry, signal conditioningcircuitry, solenoid driver circuitry, and other types of circuitry.

One or more power source control maps relating the signals frominterface devices 18, engine speed, engine fueling, and/or torque limitsmay be stored within the memory of control module 27. Each of these mapsmay be in the form of tables, graphs, and/or equations and include acompilation of data collected from lab and/or field operation ofpowertrain 16. Control module 27 may reference these maps and controlthe operation of power source 22 and bring performance of machine 10 inline with operator expectations.

An exemplary power source control map is shown in FIG. 4. In this map, atorque limit curve 400 is shown that corresponds with a maximum amountof torque that could be produced by power source 22 at any given speed.This maximum amount of torque may also correspond with a maximum amountof fuel consumed by power source 22 at the given speed. As shown in themap of FIG. 4, the neutral position of right foot pedal 18 a maycorrespond with an engine speed of about 800 rpm, and the fullydisplaced position of right foot pedal 18 a may correspond with multipledifferent engine speeds, depending on the mode of operation and theactual or desired margin between the Actual Engine Torque and theAvailable Engine Torque. For example, the fully displaced position maycorrespond with a Low Max Limit of about 1200 rpm and a High Max Limitof about 1400 rpm, when machine 10 is operating in an economy mode. Incontrast, the fully displaced position may correspond with a Low MaxLimit of about 1400 rpm and a high Max Limit of about 1600 rpm, whenmachine 10 is operating in a performance mode. Alternatively, the fullydisplaced position could correspond with a Low Max Limit of about 1200rpm and the High Max Limit of about 1600 rpm, when machine 10 isoperating in the performance mode, if desired. In general, the economymode of operation is associated with lower values for one or both of theLow and High Max Limits. For example, the Low Max Limit of the economymode may be about 75% of the performance mode High Max Limit; and theHigh Max Limit of the economy mode may be about equal to the performancemode Low Max Limit. Other relationships, however, may also be utilized.The control map of FIG. 4 will be discussed in more detail in thefollowing section.

Control module 27, together with power source 22, transmission 24, andinterface devices 18, may embody a transmission system 36. FIG. 5 is aflow chart depicting an exemplary method of operating transmissionsystem 36. FIG. 5 will be discussed further in the following section tobetter illustrate the disclosed system and its operation.

INDUSTRIAL APPLICABILITY

The disclosed transmission system may be applicable to any vehiclehaving a CVT (e.g., an electric or hydraulic CVT). In particular, bydirectly controlling both engine fueling and the torque output of amachine's powertrain, operator control of the machine may be improvedwhile also providing better overall vehicle efficiency. In addition, byproviding for selective operation within an economy mode, furthermachine efficiencies may be realized. Operation of transmission system36 will now be described with reference to the flowchart of FIG. 5.

The first step of operating transmission system 36 may include receivinga desired mode selection from the operator of machine 10, receiving adisplacement position of right foot pedal 18 a, determining the ActualEngine Torque, and determining the Available Engine Torque (Step 500).As described above, the desired mode may be selected via interfacedevice 18 b as either a performance mode of operation or an economy modeof operation. In some embodiments, the operator may be able to selectone or more increments between a maximum economy mode and a maximumperformance mode. Any number of economy modes may be available. Thedisplacement position of right foot pedal 18 a may be determined basedon signals generated by sensor 32. The Actual Engine Torque and theAvailable Engine Torque may be determined by control module 27, providedto control module 27 by a dedicated power source controller (not shown),and/or generated in another manner known in the art. For example,control module 27 may determine these values based, at least in part, onthe current fueling of power source 22 at the current engine speed andthe maximum limit of fueling at the current engine speed.

Control module 27 may determine whether the desired mode of operation isthe performance mode or one of any available economy modes (Step 505),and respond accordingly.

For example, if the desired mode of operation is the performance mode,control module 27 may set the High Max Limit of power source 22 to afirst engine speed (e.g., to Speed₁), and set the Low Max Limit of powersource 22 to a second engine speed that is less than the first enginespeed (e.g., to Speed₂<Speed₁) (Step 510). However, if the desired modeof operation is an economy mode, control module 27 may instead set theHigh Max Limit of power source 22 to a third engine speed that, in thedisclosed example, is the same as or less than the second engine speed(e.g., Speed₃<Speed₂), and set the Low Max Limit to a fourth enginespeed that is less than the third engine speed (e.g., Speed₄<Speed₃)(Step 515). In one example, Speed₁ may be a maximum rated speed of powersource 22 and about equal to 1600 rpm; Speed₂ may be about 85-90% ofSpeed₁ (i.e., about 10-15% less than Speed₁) or about 1400 rpm; Speed₃may be about equal to Speed₂ or about 1400 rpm; and Speed₄ may be about75% of Speed₁ or about 1200 rpm. Other values and relationships forSpeeds₁₋₄ may also be possible.

Control module 27 may then compare the Actual Engine Torque to theAvailable Engine Torque, to determine if the Actual Engine Torque iswithin a desired margin (e.g., within about 10%) of the Available EngineTorque (Step 520). For example, control module 27 may divide the ActualEngine Torque (i.e., current fueling of power source 22 for the givenspeed) by the Available Engine Torque (i.e., maximum fueling of powersource 22 at a maximum speed currently mapped to full right foot pedaldisplacement). If the Actual Engine Torque is about 90% or more of theAvailable Engine Torque (i.e., if there is less than a 10% marginbetween Available Engine Torque and Actual Engine Torque), control mayproceed to step 525. Otherwise, control may proceed to step 530.

At step 525, controller 27 may map the full displacement position ofright foot pedal 18 a to correspond with the High Max Limit of thedesired mode (e.g., about 1600 rpm for the performance mode and about1400 rpm for the economy mode). At step 530, controller 27 may insteadmap the full displacement position of right foot pedal 18 a tocorrespond with the Low Max Limit of the desired mode (e.g., about 1400rpm for the performance mode and about 1200 rpm for the economy mode).In both steps 525 and 530, mapping of the right foot pedal neutralposition may remain unchanged, at about 800 rpm. Several examples areprovided below to further illustrate steps 500-530.

In a first example, assume that machine 10 is operating at steady statein the performance mode, wherein the High Max Limit of power source isabout 1600 rpm and the Low Max Limit is about 1400 rpm. At this time,the speed of power source 22 may be somewhere between these values, forexample at about 1550 rpm. In this situation, the Actual Engine Torquemay be fairly close to the Available Engine Torque, for example at about95%. If machine 10 were to then encounter a decline, Actual EngineTorque (i.e., the current fueling of power source 22) may reduce and,when compared to the Available Engine Torque (i.e., the maximum amountof fueling for the current engine speed), the margin between Actual andAvailable Engine Torques may grow to more than 10%. In this situation,controller 27 may determine that control should proceed from step 520 tostep 530 and therefore reduce the speed of power source 22 correspondingto full right pedal displacement to the Low Max Limit or to about 1400rpm. In other words, when power source 22 no longer requires the higheramount of torque, controller 27 may reduce the maximum speed achievableat full right pedal displacement (and, in turn, also the amount of fueland torque available at the current engine speed) to a lower value thatconserves fuel. That is, even if the operator maintains full or nearlyfull displacement of right foot pedal 18 a, a drop in Actual EngineTorque may result in an automatic drop in the speed of power source 22and a corresponding drop in fuel consumption. In this same example, ifthe operator had instead chosen the economy mode of operation,controller 27 would have remapped full right pedal displacement fromabout 1400 rpm to about 1200 rpm.

Now assume that machine 10 encounters an incline during the performancemode of operation, and the Actual Engine Torque increases such that themargin between Actual and Available Engine Torques becomes less than thedesired margin (e.g., less than about 10%). In this situation,controller 27 may determine that control should proceed from step 520 tostep 525. That is, controller 27 may remap the full displacementposition of right pedal 18 a from the Low Max Limit of about 1400 rpm tothe High Max Limit of about 1600 rpm. In other words, as the torquerequirement of power source 22 starts to increase, controller 27 mayraise the raise the maximum speed achievable at full right pedaldisplacement (and, in turn, the maximum amount of fueling and torqueavailable at the current engine speed) to a higher value that providesmore torque. That is, even if the operator maintains full or nearly fulldisplacement of right foot pedal 18 a, an increase in Actual EngineTorque may result in an automatic increase in the speed of power source.In some instances, this may also correspond with an increase in machineperformance. In this same example, if the operator had instead chosenthe economy mode of operation, controller 27 would have instead remappedfull right pedal displacement from about 1200 rpm to about 1400 rpm.

It is contemplated that instead of a large step increase from the LowMax Limit to the High Max Limit in response to the margin between Actualand Available Engine Torques falling below about 10%, controller 27could instead increase power source speed by a smaller amount. Forexample, controller 27 could increase power source speed by about 50 rpmincrements, or increase power source speed linearly to maintain the 10%margin, if desired.

After mapping of right pedal displacement has been adjusted, controlmodule 27 may use the new mapping to adjust fueling of power source 22at the current engine speed and the current right foot pedal position.In particular, control module 27 may selectively adjust fueling of powersource 22 to correspond with values stored in the map for the currentengine speed and for the current displacement position of right footpedal 18 a. In other words, by adjusting the maximum displacementposition of right foot pedal 18 a, all positions between the neutralposition and the maximum displacement position may be automaticallyadjusted in the same direction by related amounts. In addition,controller 27 may adjust operation of transmission 24 based on thesignal generated by right foot pedal 18 a and on the map.

High machine efficiency may be realized in association with thedisclosed transmission system, as control over fueling of power source22 may not always directly correspond with operator input. Inparticular, the operator may manipulate right foot pedal 18 a withoutnecessarily causing a direct change in fueling of power source 22.Instead, displacement of right foot pedal 18 a may cause a change inmerely the gear ratio of transmission 24 and, only when the changerequires a significant increase or decrease in the amount of availabletorque from power source 22, will the displacement cause a change infueling of power source 22. However, even when this occurs, the changein fueling may be based on maintaining the desired margin of AvailableEngine Torque above the Actual Engine Torque and not directly based onthe displacement. In other words, power source fueling may be somewhatindependent of operator input, allowing for greater engine stability andlower fuel consumption.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the disclosed transmissionsystem. Other embodiments will be apparent to those skilled in the artfrom consideration of the specification and practice of the disclosedtransmission system. It is intended that the specification and examplesbe considered as exemplary only, with a true scope being indicated bythe following claims and their equivalents.

What is claimed is:
 1. A power system for use with a mobile machinehaving a traction device, comprising: a power source configured togenerate a torque output; a transmission configured to receive at leasta portion of the torque output and to drive the traction device; anoperator input device movable through a range from a neutral position toa maximum displaced position to generate a signal indicative of adesired torque of the traction device and a desired speed of the powersource; and a controller in communication with the power source, thetransmission, and the operator input device, the controller beingconfigured to: reference the signal from the operator input device witha map stored in memory to determine a corresponding speed of the powersource; determine a margin between an actual and a maximum availabletorque output of the power source at a current power source speed;selectively adjust a speed of the power source mapped to the maximumdisplaced position of the operator input device based on the margin; andselectively adjust fueling of the power source at a current displacementposition of the operator input device and operation of the transmissionbased on the signal and on the map.
 2. The power system of claim 1,wherein the controller is further configured to: receive a selectionfrom an operator of the mobile machine indicative of desired operationin a performance mode or an economy mode; and selectively lower thespeed of the power source mapped to the maximum displaced position whenthe selection is the economy mode.
 3. The power system of claim 2,wherein the controller is further configured to selectively lower aspeed of the power source mapped to the neutral position when theselection is the economy mode.
 4. The power system of claim 3, whereinthe speed of the power source mapped to maximum displaced positionduring operation in the economy mode is about the same as the speed ofthe power source mapped to the neutral position during operation in theperformance mode.
 5. The power system of claim 3, wherein the speed ofthe power source mapped to the neutral position during operation in theeconomy mode is about 75% of the speed of the power source mapped to themaximum displaced position during operation in the performance mode. 6.The power system of claim 1, wherein the controller is configured toselectively drop the speed of the power source mapped to the maximumdisplaced position when the margin increases past a threshold.
 7. Thepower system of claim 6, wherein the controller is configured toselectively drop the speed of the power source mapped to the maximumdisplaced position by about 10-15% when the margin increases past athreshold.
 8. The power system of claim 7, wherein the margin is about10%.
 9. The power system of claim 6, wherein the controller isconfigured to selectively increase the speed of the power source mappedto the maximum displaced position when the margin is about equal to orless than the threshold.
 10. The power system of claim 9, wherein thecontroller is configured to selectively increase the speed of the powersource mapped to the maximum displaced position to maintain the marginat about the threshold.
 11. The power system of claim 10, wherein thecontroller is configured to incrementally increase the speed of thepower source mapped to the maximum displaced position.
 12. The powersystem of claim 10, wherein the controller is configured to linearlyincrease the speed of the power source mapped to the maximum displacedposition.
 13. The power system of claim 10, wherein the margin is aboutequal to zero when the operator input device is moved to maximumdisplaced position.
 14. The power system of claim 10, wherein the marginis greater than the threshold when the operator input device is moved tothe neutral position.
 15. The power system of claim 1, wherein thetransmission is a continuously variable transmission.
 16. A power systemfor a mobile machine having a traction device, comprising: a powersource configured to generate a torque output; a continuously variabletransmission configured to receive at least a portion of the torqueoutput and to drive the traction device; an operator input devicemovable through a range from a neutral position to a maximum displacedposition to generate a signal indicative of a desired torque of thetraction device and a desired speed of the power source; and acontroller in communication with the power source, the continuouslyvariable transmission, and the operator input device, the controllerbeing configured to: reference the signal from the operator input devicewith a map stored in memory to determine a corresponding speed of thepower source; determine a margin between an actual and a maximumavailable torque output of the power source at a current speed;selectively adjust a speed of the power source mapped to the maximumdisplaced position of the operator input device based on the margin;selectively adjust fueling of the power source at a current displacementposition of the operator input device and operation of the continuouslyvariable transmission based on the signal and on the map; receive aselection from an operator of the mobile machine indicative of desiredoperation in a performance mode or an economy mode; and selectivelylower the speed of the power source mapped to the maximum displacedposition and a speed of the power source mapped to the neutral positionwhen the selection is the economy mode.
 17. The power system of claim16, wherein: the speed of the power source mapped to maximum displacedposition during operation in the economy mode is about the same as thespeed of the power source mapped to the neutral position duringoperation in the performance mode; and the speed of the power sourcemapped to the neutral position during operation in the economy mode isabout 75% of the speed of the power source mapped to the maximumdisplaced position during operation in the performance mode.
 18. Thepower system of claim 16, wherein the controller is configured to:selectively drop the speed of the power source mapped to the maximumdisplaced position when the margin increases past a threshold; andselectively increase the speed of the power source mapped to the maximumdisplaced position when the margin is about equal to or less than thethreshold.
 19. The power system of claim 18, wherein: the margin isabout equal to zero when the operator input device is moved to maximumdisplaced position; and the margin is greater than the threshold whenthe operator input device is moved to the neutral position.
 20. A methodof operating a mobile machine having a traction device driven by a powersource via a transmission, the method comprising: determining adisplacement position of an operator input device that is indicative ofa desired torque of the traction device and a desired speed of the powersource referencing the displacement position with a map to determine acorresponding speed of the power source; determining a margin between anactual and a maximum available torque output of the power source at acurrent speed; selectively adjusting a speed of the power source mappedto the maximum displaced position of the operator input device based onthe margin; selectively adjusting fueling of the power source at acurrent displacement position of the operator input device and operationof the transmission based on the signal and on the map; receiving aselection from an operator of the mobile machine indicative of desiredoperation in a performance mode or an economy mode; and selectivelylowering the speed of the power source mapped to the maximum displacedposition of the operator input device and a speed of the power sourcemapped to a neutral position of the operator input device when theselection is the economy mode.